In one aspect of this invention, the invention considers the anatomical shape of the area of the patient being operated on and tailors the shape of the dilators and the dilator retractor or cannula to accommodate that shape. In another aspect of this invention, the invention constitutes an improvement over the apparatus and method disclosed and claimed in U.S. Pat. No. 6,159,179 granted on Dec. 12, 2000 to the inventor of this patent application and entitled “Cannula and Sizing and Insertion Method” by providing different sizes of the same configuration of dilator retractors.
As is well known by those skilled in this technology, the cannula utilized in the field of minimally invasive surgery is particularly efficacious in performing such spinal medical procedures as laminotomy, medial facetectomy, foraminotomy, nerve root retraction, discectomy and the like, is cylindrically shaped. I have found that a cylindrically shaped cannula is not always ideal for certain surgical procedures and this invention is intended to obviate the problems incidental to a cylindrically shaped cannula and to increase the number of surgical procedures that can be performed by dilation methods by changing the configuration of the retractor tube or cannula. As is apparent to one skilled in this technology, the anatomy of the human spine is not made up of flat surfaces and a purely cylindrical device passed over cylindrical dilators and directed toward the lamina more likely than not settles off of or partly on the bone. When this occurs, a tuft of muscle migrates to or is left between the bone and the bottom of the retractor and must be removed surgically. Obviously, this surgery is a source of pain and discomfort for the patient and creates an additional surgical step for the surgeon. Moreover, this additional surgery causes additional bleeding and as a consequence, creates an obstruction to the vision of the surgeon. In order to cure the obstruction, the surgeon must address this problem through an electro cautery procedure.
Also apparent to one skilled in this technology is that the pathological target within the patient is often not an equal distance vertically and horizontally. Hence, a surgical procedure may require a surgical approach that for ideal conditions, provides access that is more vertical in orientation than lateral. Obviously, a cylindrical device as has been heretofore available and as disclosed in U.S. Pat. No. 6,159,179 supra, which is equidistant from the axis, does not allow for this approach. Thus, in a cylindrical cannula, in order to gain additional vertical access the size of the cannula must be increased the same amount in the lateral direction that it is in the vertical direction. Obviously, the human spine's skeletal structure, i.e. lateral facets and medial spinous process, restricts the amount of lateral space available. In a cylindrical cannula, since a limitation of the lateral space that is available to locate a retractor, the vertical space is likewise limited. As a consequence, the cylindrical cannula limits the number of patients who are candidates for minimally invasive spinal surgery necessitating the more invasive type surgery with all of the problems associated therewith. Hence, for a large segment of the patient population, the only surgery available is the more destructive invasive muscle burning and stripping approach. This invention addresses this problem and provides a solution whereby the minimal invasive surgery is now possible which otherwise was considered impossible to perform, unpractical or unpredictable in terms of surgical success or long-term outcome.
The other aspect of this invention is the improvement to the system claimed in U.S. Pat. No. 6,159,179, supra. In this patent, the depth of the cavity at the location where the invasive procedure is being performed is measured and the surgeon can then select from a kit or inventory of different sized cannulas or retractors the desired size required to perform the surgical procedure.
I have found that a solution to the problem noted in the immediate above paragraphs is that I provide in one embodiment of this invention, dilators and retractors that are configured other than in a cylindrical shape, such as an ovoid, and that I provide different sizes to meet the anatomical needs of a particular patient. By providing dilators and dilator retractors made in accordance with this invention, these instruments will be able to reach down between the facet joint and the spinous process to gently part muscle tissue and come into closer contact to the bony target. This will reduce or eliminate the need for the surgeon to surgically remove otherwise valuable viable muscle tissue. This will also reduce post-operative pain and inter-operative time (fiddle). In addition to the above, this new design will allow surgeons to address new pathologies in patients that previously would not have been able to undergo a minimally invasive technique. To more fully appreciate the importance of this invention a common example is discussed immediately hereinbelow.
This example considers a patient with multilevel central canal stenosis. To address this patient's pathology, the surgeon may need over 35 millimeters (mm) of vertical access. The typical lateral distance, i.e., space between the spinous process and the facet joint, available at the L4 lamina is 16 mm. A 16 mm cylindrical retractor would fit tightly against the lamina but even with “wanding” (moving up and down) it would restrict the surgeons ability to reach much more than the 16 mm in vertical access. The only option that is available to the surgeon, heretofore, is to utilize a cylindrical retractor. As explained above, since the equation for a cylindrical retractor mandates that the lateral and vertical expansions are equal, the cylindrical retractor would quickly reach beyond the practical or acceptable size for many, if not most, multilevel patient candidates.
Another embodiment of this invention is the contouring or configuring of the bottom of the retractor in order to meet the requirements of certain operation procedures and/or permit the retractor to be positioned closer to the target. This invention contemplates angling the tip in both a cylindrical and ovoid shaped retractor and/or locating a tunnel in the bottom thereof which allows for a rod or implant to be passed through the distal tip of the cannula and into a pedicle screw (e.g., as shown in FIG. 5A).
While much has been accomplished in the medical field to limit tissue disruption, use minimal incisions, reduce the hospital stay and increase the speed in which the patient recovers, this invention is intended to raise the surgical procedure to a higher level. This invention in the field of minimally invasive surgery is particularly efficacious in performing such spinal medical procedures as laminotomy, medial facetectomy, foraminotomy, nerve root retraction, discectomy and the like.
As discussed in U.S. Pat. No. 6,159,179, supra, a typical procedure in performing a lumbar discectomy is to advance a guidewire through a small incision which is advanced to the inferior edge of the superior lamina. A small incision is then made that extends either cranially or caudally. A dilator is then inserted over the guidewire. Larger diameter dilators are sequentially inserted over each other to increase the opening into the body cavity. Typically the guide wire is removed after the first dilator is installed and eventually the dilators are all removed after the tubular retractor has been inserted over the largest of the dilators. Once these procedures are accomplished, the retractor is locked into position by a retractor clamp that is clamped to a retractor clamping arm which is fixed to a rigid member such as the operating table. This provides an unencumbered zone where the surgeon can perform the medical procedure that was intended to be performed. According to the present invention, the dilators, of course will now conform to the configuration discussed above.
Instead of sizing the cannula to the largest depth that is anticipated in the surgical procedure, the U.S. Pat. No. 6,159,179 patent, supra, teaches providing to the surgeon a series of different sizes in a kit so that the surgeon can measure the depth of the cavity of the patient and select the requisite size from the kit. Hence, the surgeon measures the depth by measuring from the exterior of the cavity to the most interior position in the cavity (inferior edge of the superior lamina) and then selects, for example, either a 10 millimeters (mm), 20 mm, 30 mm, etc. as the situation requires. The dilator retractor will also have the same cross sectional shape as the dilator, but it may have a predetermined configuration at the distal end. This invention improves the state of the art of spinal surgery by expanding the current boundaries of minimally invasive surgery. This provides a new option to patients that would otherwise be delegated to the more disruptive open muscle stripping surgical approaches. The ovoid design with or without the angled distal tip, allows a surgeon greater vertical access without having to be encumbered by unnecessary lateral access.
Also, it is contemplated within the scope of this invention, that the dilator retractor will be provided in a kit where a given configuration will be provided in a series of dilator retractors that have different lengths, so that the depth of the cavity of the patient will determine the particular sized dilator retractor that will be utilized for that procedure.